The electrical properties of excitable cells are determined in large part by the voltage-gated K+ channels, i.e., xe2x80x9cKv channelsxe2x80x9d, present on the plasma membrane of such cells. Kv channels are also important in many nonexcitable cells where they contribute to diverse processes such as volume regulation, hormone secretion, and activation by mitogens. At least 50 different Kv channel genes have been identified, and most have been assigned to one of the following four major subfamilies: Kv1, Kv2, Kv3, and Kv4. Each Kv channel gene encodes a single pore-forming subunit, referred to as the xcex1-subunit. Functional Kv channels are formed by the tetrameric association of individual xcex1-subunits. With multiple Kvxcex1 proteins that assemble as multi-subunit heteromeric complexes, there may be hundreds of functionally distinct Kv channels.
Kv channels, either functioning or malfunctioning, are implicated in many disease states including cardiac arrhythmias, hypertension, angina, asthma, diabetes, renal insufficiency, urinary incontinence, irritable colon, epilepsy, cerebrovascular ischemia and autoimmune diseases. Accordingly, efforts are underway to identify and characterize pharmacological agents that alter the kinetics, gating or formation of Kv channels. The efficacy of such agents is determined by treating cells with such agents and measuring changes in current across the plasma membrane of the cells. Unfortunately, it is difficult to measure small changes in the current in most cells. It is also difficult to determine whether a pharmacological agent alters current flow through a specific Kv channel. Accordingly, it is desirable to have methods and tools which can be used to regulate the numbers and types of Kv channels on the plasma membrane of cells. It is also desirable to have new research tools that can be used for examining the assembly and synthesis of Kv channels.
The present invention provides novel polynucleotides that encode a novel protein, designated herein as K+ Channel Associated Protein or xe2x80x9cKChAPxe2x80x9d. It has been determined that expressing polynucleotides that encode KChAP in host cells, along with polynucleotides that encode the Kvxcex1 channel subunit Kv 2.1, the Kvxcex1 channel subunit Kv 2.2, the Kvxcex1 channel subunit Kv 1.3, or the Kvxcex1 channel subunit Kv 4.3, increases the number of Kv2.1, Kv 2.2, Kv1.3 or Kv4.3 channels, respectively, in the plasma membrane of such cells. Accordingly, KChAP polynucleotides are useful for making cells that have increased numbers of Kv channels on the cellular plasma membrane. Such cells are useful model systems for studying the effect of pharmacological agents on Kv channels, particularly on Kv2.1, Kv 2.2, Kv 1.3, and Kv 4.3 channels.
The present invention also relates to the novel protein KChAP. During formation of Kv channels, KChAP binds to the Kvxcex1 channel subunits Kv2.1, Kv2.2, Kv1.3, and Kv4.3 within the cytoplasm of the cell. KChAP also binds to the Kvxcex1 channel subunits Kv1.2, Kv 1.4, Kv1.5 and Kv 3.1 and to Kvxcex2 subunits. Accordingly, KChAP and the antibodies that are immunospecific for KChAP are useful research tools for monitoring the interaction between diverse Kvxcex1 channel subunits and KChAP and for monitoring the interaction between Kvxcex1 subunits and Kvxcex2 subunits.